The present invention relates generally to flexible abrasive products which comprise an abrasive coating on a substrate which includes multiple separated but connected bodies which are spaced apart to provide openings through the substrate.
The usual objective of any sanding operation is to remove unwanted material from the surface being sanded and to prepare that surface for subsequent coating operations. Typically, these two objectives are diametrically opposed. Removing unwanted material from the surface in a reasonable amount of time requires the use of a coarse abrasive while preparing the surface for subsequent coating operations requires the use of a fine abrasive. Thus, the operator must sand the surface multiple times with a succession of increasingly finer grit sandpaper to achieve both objectives. The coarse sandpaper removes unwanted material quickly. However, a progression of increasingly finer sandpaper is often needed to remove the unacceptably deep scratches left in the surface by the coarse sandpaper. This entire sanding process is viewed by many as laborious, time consuming, and generally distasteful. Sandpaper manufacturers recognize this dilemma and have offered many products in an attempt to solve the problem.
Conventional sandpaper is normally manufactured by adhering abrasive mineral particles to a thin relatively stiff, non-porous paper backing with a relatively inflexible adhesive. This construction yields a product with good initial stock removal (cut) but with a deep scratch pattern and the product has an undesirable relatively short life. The stock removal and deep scratch characteristics of conventional sandpaper can be attributed to the relatively stiff nature of the product. Further, the non-porous nature of the backing contributes to the short life of conventional sandpaper by trapping the debris generated during sanding. This trapped debris often clogs the abrading surface of the sandpaper preventing any further stock removal. Additionally, the thin, slippery nature of conventional sandpaper makes the product difficult to hold and use.
While such flat sandpapers are widely successfully used in a multitude of commercial applications, abrasive manufacturers such as Minnesota Mining and Manufacturing Company (3M) have recognized the above-noted deficiencies with conventional sandpaper and introduced other types of sanding products in an attempt to solve the above noted problems. 3M introduced an abrasive coated sponge under the trade designation SMALL AREA SANDING SPONGE Catalog #907, as an example of such a product. Conventional sanding sponge products are normally manufactured by adhering abrasive mineral particles to a relatively thick synthetic foam backing with a relatively flexible adhesive. The finished sanding sponge is usually between 5 mm and 25 mm thick with a non-porous abrasive surface on all major surfaces. The flexible nature of this product construction yields a finer scratch pattern in the sanded surface than conventional sandpaper when comparable grit size products are used to sand the same surface while the thickness of the construction allows easier gripping and more comfortable use. However, the flexible nature of conventional sanding sponges decreases the stock removal (cut). Like conventional sandpaper, the non-porous surface of a conventional sanding sponge traps the dust generated during sanding which may clog the abrasive surface minimizing future stock removal.
U.S. Pat. No. 2,984,052 (Mueller, Jr.) discloses coated abrasive product comprising an open, woven or knit mesh fabric having a plurality of protrubences regularly spaced throughout or regularly spaced raised areas with abrasive grains bonded thereto with the remainder of the backing sheet being free of bonded abrasive grains.
U.S. Pat. No. 5,578,343 (Gaeta et al.) discloses a mesh-backed abrasive material which comprises an unfinished greige mesh fabric in which at least 20% of the surface area is voids and which is coated with a maker coat of binder to attach abrasive grain thereto and overcoated with a size coating of binder to provide an abrasive product.
U.S. Pat. No. 5,637,386 (Darjee) discloses a coated abrasive comprising a substrate selected from woven and knit materials such as an elastic knit fabric and abrasive particles bonded directly to the substrate in a spaced discontinuous pattern.
German Utility Model No. DE 201 11 245 U1, published Jun. 21, 2001, discloses a sanding cloth made by adhering abrasive particles to a textile structure with many openings.
U.S. Pat. No. 6,099,776 (Tintelnot) discloses a flexible, open-pored cleaning body having at least one scouring surface with continuously formed raised projecting ridges of different heights which may have abrasive grain embedded therein.
Notwithstanding the above disclosures, there remains a need for a highly conformable abrasive product which will not easily become clogged with the debris created by sanding operations.
The present invention provides a flexible abrasive product which is easily conformable to contoured surfaces being abraded, easily held by hand and may be used with sanding devices, yet will not easily clog with the debris created by typical abrading operations.
In one aspect the invention provides a flexible abrasive product comprising:
a. a flexible sheet-like substrate comprising a multiplicity of separated resilient bodies connected to each other in a generally planar array in a pattern which provides open spaces between adjacent connected bodies, each body having a first surface and an opposite second surface; and
b. abrasive particles to cause at least said first surface to be an abrasive surface.
Preferred flexible abrasive products include bodies which are generally square and bodies wherein the first surface is a convex surface. Preferred resilient bodies are comprised of an elastomeric material such as foam rubber composition.
The preferred manner in which to provide the abrasive surface is by coating the first surface with a curable make binder coating, applying abrasive grains to the uncured make binder coating and at least partially curing the make binder coating. A preferred embodiment includes applying a size coating over the make binder coating and abrasive particles and fully curing the coatings to firmly adhere the abrasive particles in the abrasive coating.
In a further aspect, the invention provides a method for making a flexible abrasive product comprising:
a. providing a flexible sheet-like substrate comprising a multiplicity of separated resilient bodies connected to each other in a generally planar array in a pattern which provides open spaces between adjacent connected bodies, each body having a first surface and an opposite second surface; and
b. providing abrasive particles to at least said first surface to provide an abrasive surface.
A preferred method of providing the abrasive surface is provided by coating the first surface with a make coating of curable binder composition, depositing abrasive particles onto the make coating of the curable composition and at least partially curing the make coating composition. It is also preferred to coat the make coating and abrasive particles with a size coating of a curable composition and curing the size coating composition.
An alternate preferred method of providing abrasive particles to the first surface is by mixing abrasive particles with a curable binder composition to provide a mixture which cures to provide an abrasive coating, coating the first surface with the mixture and curing the curable binder composition. Preferably, after coating but prior to curing, the curable binder composition containing abrasive particles is contacted with a surface of a tool which includes raised areas and depressed areas to provide a shaped or structured surface to the abrasive coating.
The above method of providing a shaped or structured abrasive coating is described in U.S. Pat. No. 5,435,816 assigned to the same assignee as the present patent application. This patent is incorporated herein by reference.
The present invention provides an abrasive article that has an improved cut-rate. xe2x80x9cCut-ratexe2x80x9d refers to the ability of an abrasive product to remove material or surface particles from the surface of a workpiece. The cut-rate is the amount of weight loss from the workpiece per unit of time. The abrasive product of the invention also has an improved scratch pattern when compared to the scratch pattern of conventional sandpaper or conventional sanding sponges. These results are surprising and unexpected for a number of reasons.
First, the surface of flexible abrasive article of the invention has an abrading surface which is non-continuous because the article is composed of a multitude of small separate typically rectangular resilient bodies (or pillows) connected to each other at corners to form an open mat. The resilient bodies are arranged in a generally checkerboard pattern such that a small open space (typically approximately the same size as the resilient bodies) is adjacent to each side of the bodies. Once coated with abrasive mineral, this arrangement results in an abrasive article with an abrasive surface having a relatively large total abrasive area separated on individual body surfaces by openings to provide a somewhat smaller total open area. By contrast, conventional sandpaper is typically coated on a continuous backing composed of approximately 100% abrasive surface and 0% open space. One skilled in the art of sandpaper would expect the cut-rate of the flexible abrasive article of the present invention to be less than the cut-rate of conventional sandpaper by virtue of the fact that conventional sandpaper contains a continuous abrasive surface. Surprisingly, this is not the case. It has been found in paint sanding tests that the product of the invention is substantially equivalent to or slightly better in cut-rate than conventional sandpaper. This surprising result may be explained by the anti-clogging nature of the open flexible abrasive article of the invention because of the openness which permits easy removal of swarf. xe2x80x9cSwarfxe2x80x9d refers to the fine particles that are created during the abrading process.
The open spaces adjacent to each resilient bodies serve as reservoirs to collect the dust generated during the sanding process, effectively removing the sanding dust from the abrasive surface, resulting in less abrasive surface clogging and higher stock removal than expected.
Second, the foam-like nature of the flexible substrate of the abrasive article of the present invention provides a fine scratch pattern in the sanded surface. Abrasive minerals coated on foam-like backings will leave a finer scratch pattern in the sanded surface than conventional sandpaper having abrasive of comparable grit size. One skilled in the art of sandpaper would not expect the scratch finish pattern left in the sanded surface by the present invention to be substantially different from that left by a conventional sanding sponge of comparable grit size. Surprisingly, the results of the scratch finish testing of the abrasive article of the present invention and a conventional sanding sponge demonstrate that a significantly finer scratch pattern is left in the sanded surface by the flexible abrasive article of the invention than a conventional sanding sponge of comparable abrasive grit. These results can be explained by the checkerboard arrangement of small abrasive coated resilient bodies. Each of the abrasive coated resilient bodies is essentially a small sanding sponge which collectively provide a unique unexpected result. However, the checkerboard arrangement of the abrasive coated resilient bodies also contributes to the fine finish left in the sanded surface. Since each abrasive coated resilient body is connected to an adjacent abrasive coated resilient body with an inherently flexible joint, each abrasive coated resilient body is free to follow a slightly different path across the sanded surface. This results in multiple, overlapping sanding paths with a fine scratch finish. The multitude of small resilient bodies in the flexible abrasive product of the invention result in a multitude of sanding paths when the abrasive article is deployed over the surface being abraded. Many of the individual sanding paths will overlap each other during the surface finishing process yielding an unexpectedly fine sanding scratch pattern.
xe2x80x9cflexiblexe2x80x9d in reference to the flexible abrasive product of the invention means that the abrasive product is sufficiently conformable to be folded over on itself without permanent deformation and will substantially redeploy to its original structure when unfolded.
xe2x80x9cresilientxe2x80x9d with reference to the resilient bodies is intended to refer to the material from which the bodies are formed which is sufficiently compressible to be deformed under pressure yet will return to its original configuration when the pressure is removed.
xe2x80x9cconvexxe2x80x9d in reference to the preferred configuration of the first surface of the resilient bodies is intended to indicate that the first surface has a high point which is distally spaced from the peripheral surface adjacent the edges of the resilient body on the same side.
xe2x80x9cacrylatexe2x80x9d and xe2x80x9cpolyfunctional acrylatexe2x80x9d are meant to include substituted acrylates such as methacrylates as well. xe2x80x9cactinic radiationxe2x80x9d means non-particulate radiation having a wavelength within the range of 200 to 700 nanometers.
xe2x80x9caverage acrylate functionalityxe2x80x9d refers to the average number of acryloxy groups per molecule; it is determined by dividing the total number of acryloxy groups in the polyfunctional acrylate by the total number of molecules of polyfunctional acrylate.
xe2x80x9caverage epoxy functionalityxe2x80x9d refers to the average number of epoxy groups per molecule; it is determined by dividing the total number of epoxy groups in the epoxy resin by the total number of epoxy resin molecules.
xe2x80x9cbireactive compoundsxe2x80x9d are those which contain at least one ethylenically-unsaturated group and at least one 1,2-epoxide group.
xe2x80x9cepoxy resinxe2x80x9d refers to a composition comprising at least one compound having at least one epoxy group.
xe2x80x9cepoxy groupxe2x80x9d refers to an oxiranyl group.
xe2x80x9cmonofunctional acrylatexe2x80x9d refers to a compound having one acryloxy group per molecule.
xe2x80x9cphotoinitiatorxe2x80x9d refers to a substance which, when exposed to light, is capable of polymerizing polymerizable groups; the polymerization may be free radical or cationic in nature.
xe2x80x9cpolyfunctional acrylatexe2x80x9d refers to a compound having an acryloxy functionality of greater than 1.
xe2x80x9cpolyolxe2x80x9d refers to a compound having a hydroxyl functionality greater than 1.